Field of the Invention
The present invention relates to a real-time type network facsimile machine that executes facsimile communications based on the ITU-T recommendation T.38 and uses the SIP (Session Initiation Protocol) for call connection, a control method therefor, and a storage medium storing a control program therefor.
Description of the Related Art
Network facsimile machines that are equipped with the IPFAX communication function based on the SIP and the T.38 using an IP network are being spread in recent years. The SIP is a call control protocol for communicating multimedia, such as various sound, data, and images, on the IP network specified by the RFC 3261. The T.38 is one of recommendations of the ITU-T, and is a standard that specifies a method for translating a facsimile signal used in a subscriber telephone network into an IP message and for communicating. There are a method for connecting to a remote machine via a SIP server and a method for connecting a remote machine bypassing a SIP server, for an IPFAX communication in such a network facsimile machine. It should be noted that a SIP server associates a telephone number with an IP address using the SIP, and performs a call control for calling a remote machine and connecting with it.
One of the above-mentioned two methods is selected according to a setting of “Use of SIP server” registered in a machine. In a case where the setting of “Use of SIP server” is invalid, when an IP address is inputted as a destination, an IP message is transmitted to the destination specified by the IP address. Moreover, when a domain name is inputted as a destination, an IP address registered in a DNS server is obtained, and an IP message is transmitted to the destination specified by the IP address.
On the other hand, when the setting of “Use of SIP server” is valid, an IP message is transmitted to the destination specified by the IP address of the SIP server registered in the machine regardless of an inputted destination. When an address of destination is solved, the SIP server transmits an IP message to the solved IP address (for example, see Japanese Laid-Open Patent Publication (Kokai) No. 2012-90220 (JP 2012-90220A)).
When the above-mentioned conventional network facsimile machine performs an IPFAX communication via a SIP server, a SIP URI is inserted into a “To header” field of a SIP message, and “INVITE” is transmitted to the SIP server. The SIP URI is denoted by forms, such as “sip:2222@192.168.1.11” and “sips:user@hoge.co.jp”, for example. A character string located between “sip(sips):” and “@” is called a user part. An IP address, a host name, a domain name, or the like is described below “@”. It should be noted that the user part is omissible.
When receiving this SIP message “INVITE”, the SIP server specifies the IP address registered corresponding to “2222” that is the user part of the SIP URI, for example, and transmits the SIP message “INVITE” to the destination specified by this IP address. When a message is transmitted via a SIP server, it is necessary that the message “INVITE” includes a telephone number of a remote machine, an IP address, a user name, a domain name, etc. that are registered in the SIP server beforehand.
However, not all of a telephone number, an IP address, a user name, a domain name, etc. have been registered in a SIP server. For example, even if a user designates an IP address as a destination and transmits a message to a SIP server, the SIP server cannot connect with the remote machine because the SIP server cannot solve the address when the IP address is not registered in the SIP server.